Conventionally, adjustment of an angle of inclination of a swash plate in a variable displacement piston machine is done via an operating plunger which is in contact with the swash plate so that the movement of the operating plunger causes inclination of the swash plate.
To determine the displacement, various attempts have been made to sense the angle of inclination of the swash plate. In U.S. Pat. No. 6,209,825, an arm of a potentiometer senses the position of a piston rod. The piston is moved by a pressure in two conduits which extend into the housing of the piston pump. The piston which moves the potentiometer is a separate piston which is introduced for sensing purpose only, and the disclosed structure is therefore relatively expensive and requires interaction with the piston pump via the two conduits. This makes the structure of the piston pump more complicated and sensitive to faults in the transmission of the signal between swash plate potentiometer and the separate sensing piston.
A compressor with variable compression rate is disclosed in U.S. Pat. No. 4,822,252. Also in this case, the capacity is varied in accordance with the inclination angle of a wobble plate, and a magnetic sensor is attached to detect this angle. The sensor has a base plate fixed on a sensing housing which is fixed to the cover housing of the compressor via a washer. The sensor senses a position of a slider which is introduced in the housing merely for sensing purposes.